1. Field of the Invention
The present invention relates to a motor actuator.
2. Description of Related Art
A previously proposed motor actuator includes an electric motor and a speed reducing gear mechanism. The motor generates a drive force (motor torque) upon receiving electric power, and the speed reducing gear mechanism uses the motor torque of the motor to drive a fluid control valve. This motor actuator further includes a housing, in which a motor receiving hole is formed. The motor is installed into the motor receiving hole through a motor installation opening of the motor receiving hole and is securely supported by the housing. Here, at the time of installing the motor into the interior of the housing, a rear end part and a front end part of the motor are inserted in this order into the interior of the motor receiving hole through the motor installation opening. Thereafter, a motor fitting hole of a metal plate is fitted around a small diameter protrusion (a front bearing holder) provided at the front end side of the motor, and then the metal plate is fixed to the housing through use of fixing elements. Thus, when the engine vibration is transmitted to the motor through the metal plate, the motor is disadvantageously vibrated in the radial direction in the housing.
With reference to FIGS. 5A and 5B, in order to reduce the vibration in the radial direction of the motor, which is securely supported in the housing, it has been proposed to provide a plate type resilient member 105, which resiliently supports the motor 101 in the radial direction (the radial direction of the motor 101) that is perpendicular to the axial direction of the motor 101, in a gap between an outer peripheral surface of a small diameter protrusion (a bearing holder) 103 provided at a rear end side of the motor 101 (see, for example, Japanese Unexamined Patent Publication No. H10-252510 corresponding to U.S. Pat. No. 5,979,405 and Japanese Unexamined Patent Publication No. 2004-153914).
However, in the above motor actuator, when the plate type resilient member 105 is placed in the gap between the inner peripheral wall surface of the housing 104 and the outer peripheral surface of the small diameter protrusion 103 provided at the rear end side of the motor 101, the plate type resilient member 105 is hidden by the motor 101 and the housing 104. Thus, the assembling operation needs to be carried out in the state where the plate type resilient member 105 cannot be seen through the motor installation opening, which is the opening of the housing 104. As a result, after the installation of the motor 101 into the interior of the housing 104, it is difficult to determine whether the plate type resilient member 105 is properly installed to a predetermined installation position of the motor 101 or of the housing 104, thereby resulting in the reduced reliability of the installation operation of the plate type resilient member 105.
In view of the above disadvantage, there has been proposed another motor actuator, in which the plate type resilient member 105 is preinstalled to the motor 101 before the installation of the plate type resilient member 105 into the housing 104, and visual check of an installation state of the motor 101 and the plate type resilient member 105 is enabled to allow check of an abnormality after the installaton of the motor 101 and the plate type resilient member 105 into the interior of the housing 104 (see, for example, Japanese Unexamined Patent Publication No. 2005-180342 corresponding to EP 1544438A2).
However, similar to the motor actuator shown in FIGS. 5A and 5B, in this motor actuator, the plate type resilient member 105 is placed to circumferentially surround the small diameter protrusion 103 provided at the rear end side of the motor 101, as shown in FIG. 6. Thus, when the motor shaft 106 is vibrated in the radial direction of the motor 101 due to the vibration of the motor 101, the stress is applied to each of the front and rear bearing members (bearings), which are spaced from each other in the axial direction of the motor 101. In this way, the stress is concentrated in the root of each of the small diameter protrusions 102, 103 of the motor 101, so that the small diameter protrusions 102, 103 provided at the front and rear end sides of the motor 101 may possibly be damaged, thereby resulting in a reduction in the durability and reliability of the motor 101.
Furthermore, in the motor actuator, size variations in the outer diameter of the motor 101 generally exist due to the component tolerance and the product tolerance of the motor 101. In this case, due to the size variations in the outer diameter of the motor 101, a positional deviation may possibly be generated between a centering position at the front end side of the motor 101 and a centering position at the rear end side of the motor 101. This may result in tilting of the central axis of the motor shaft 106 of the motor 101 relative to the normal center axis or may result in a change in a shaft-to-shaft distance between the motor shaft 106 of the motor 101 and a gear shaft 110 of a speed reducing gear 109, which is meshed with a motor gear 107 that is fixed to the motor shaft 106. In this way, improper engagement may occur between the motor gear 107 and the speed reducing gear 109, so that the motor torque of the motor 101 cannot be efficiently transmitted to a valve shaft 112 of a valve element (valve) 111 of a fluid control valve. Therefore, performance of the motor actuator, particularly the drive force transmission function of the motor actuator is disadvantageously deteriorated.